83 lines
1.8 KiB
C
83 lines
1.8 KiB
C
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#include <util/atomic.h>
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#include "uart.h"
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#define UART_BUFSIZE 64
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typedef volatile struct {
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char data[UART_BUFSIZE];
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uint8_t r;
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uint8_t w;
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} buf;
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buf __attribute__ ((section (".noinit"))) uart_rxbuf;
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buf __attribute__ ((section (".noinit"))) uart_txbuf;
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#define BAUD_PRESCALE (((F_CPU/(BAUDRATE*8UL)))-1)
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void __attribute__ ((naked)) __attribute__ ((section (".init5"))) uart_init() {
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uart_rxbuf.r = 0;
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uart_rxbuf.w = 0;
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uart_txbuf.r = 0;
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uart_txbuf.w = 0;
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UCSR0A = (1<<U2X0);
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UCSR0B = (1<<RXEN0) | (1<<TXEN0) | (1<<RXCIE0);
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UCSR0C = (1<<UCSZ00) | (1<<UCSZ01); // 8N1
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UBRR0 = BAUD_PRESCALE;
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}
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void __attribute__ ((naked)) __attribute__ ((section (".fini5"))) uart_deinit() {
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while ((UCSR0B & (1 << UDRIE0))) {};
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while (!(UCSR0A & (1 << TXC0))) {};
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}
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// RX Facilities
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ISR(USART_RX_vect) {
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uint8_t c = UDR0;
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if (((uart_rxbuf.w - uart_rxbuf.r) & (UART_BUFSIZE - 1)) == 1) return;
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uart_rxbuf.data[uart_rxbuf.w++] = c;
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uart_rxbuf.w = uart_rxbuf.w & (UART_BUFSIZE - 1);
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}
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uint8_t uart_getc() {
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uint8_t c;
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while (uart_rxbuf.w == uart_rxbuf.r) {};
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// Disable interrupt to avoid race condition
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ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
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c = uart_rxbuf.data[uart_rxbuf.r++];
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uart_rxbuf.r = uart_rxbuf.r & (UART_BUFSIZE - 1);
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}
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return c;
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}
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// TX Facilities
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ISR(USART_UDRE_vect) {
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if ((uart_txbuf.w != uart_txbuf.r) && (UCSR0B & (1<<TXEN0))) {
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UDR0 = uart_txbuf.data[uart_txbuf.r++];
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uart_txbuf.r = uart_txbuf.r & (UART_BUFSIZE - 1);
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} else {
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UCSR0B &= ~(1<<UDRIE0); // UDRE off
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}
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}
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uint8_t uart_putc(unsigned char c) {
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while (((uart_txbuf.r - uart_txbuf.w) & (UART_BUFSIZE - 1)) == 1) {};
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ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
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uart_txbuf.data[uart_txbuf.w++] = c;
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uart_txbuf.w = uart_txbuf.w & (UART_BUFSIZE - 1);
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}
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UCSR0B |= (1<<UDRIE0); // UDRE on
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return 1;
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}
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